The Hypersonic Flight In the Turbulent Stratosphere (HYFLITS) research team was formed in 2016 and is currently funded by the AFOSR's Multidisciplinary Research Program of the University Research Initiative (MURI) grant, "Integrated Measurement and Modeling Characterization of Stratospheric Turbulence," awarded by the AFOSR’s High-Speed Aerodynamics Research Area in December 2017.

The multidisciplinary HYFLITS team is composed of experts in the fields of in-situ atmospheric measurements and analysis, atmospheric modeling and forecasting, and aerothermodynamics and aero-optical modeling. Our goal is to ask and resolve questions related to how future hypersonic vehicle designs can account for the effects of ambient atmospheric turbulence and particles in the middle stratosphere.

 


  • Identify and quantify the dynamics accounting for stratospheric turbulence sources, characteristics, intensities, and their statistical dependence on the meteorology below

  • Resolve uncertainties regarding small- and larger-scale turbulence impacts on hypersonic vehicle boundary layers and aero-optical systems

  • Establish critical particle concentration levels that may drive transition to turbulence in hypersonic boundary layers

  • Define the methodologies required for comprehensive, measurement- and physics-based, stratospheric turbulence forecasting, including a “strawman” forecasting system design 


OBJECTIVE: Use high-altitude balloons for in-situ measurements to characterize turbulent velocity, temperature fluctuations, and particulate concentration and size distribution in upper stratosphere.

Balloon Bus Performance (ERAU)

  • Evaluating 2-balloon solution; descent comparable to IAP flights

  • Communication link to 170 km, 6-h flight 

2-Balloon Solution

Particle Detector Deployment (UMN)

  • Focused on Alphasense particulate sensor

  • Calibrated in UMN Particle Technology Lab

UMN Particle Technology Lab

Balloon Flights (UMN)

  • 10 flights to date; more scheduled for Fall 2018

  • Developing reliable approach to reach 35+ km, descend slowly

  • Double-balloon with cutaway is current best approach

HASP Balloon Flight (UMN)

  • Alphasense sensor flown on NASA HASP

  • Obtained 9 hours of data at 125 kft (38 km)

  • Working to obtain calibrated particulate counts

  • Plan to fly more sophisticated payload on next year's flight

HASP Balloon launch

Fine-Wire Probe Development (CU)

  • Bandwidth increase for hotwire (velocity), coldwire (temperature) with constant-temperature control method

  • Adjustable gain/excitation for in-flight density variations

  • Prototype testing for LITOS comparison, Nov 2018

Fine-wire Probe

High-Altitude Calibration Tunnel (CU)

  • Initial construction completed Sep 2018

  • First calibration experiments in Nov 2018

High Altitude Calibration Tunnel

 


OBJECTIVE: CFD for multi-scale modeling of gravity waves coupled with high-resolution simulations of instabilities and small-scale turbulence -- "Sources to Turbulence"

Atmospheric Deep Compressible Model (ERA)

  • Model gravity wave sources of stratospheric turbulence
  • Provides guidance for high-resolution spectral model

Figure 4 Graph

Atmospheric Spectral Model (ERAU)

  • Provides turbulence fields at very small scales
  • Provides spatially, temporally varying inputs to US3D hypersonic bouncary layer simulations

Figure 5 Graph

Computational Aerothermodynamics (UMN)

  • Progress imposing spectral model turbulence data as inflow to US3D simulations
  • Validated reading of DNS dataset providing CFD fluctuating inflow boundary condition 

 

Aero-Optics (CU)

  • Upgraded, field-tested data-acquisition system to collect in-situ measurements of optical turbulence
  • Field-tested frame-grabber multiple digital cameras attached to astronomical telescopes
  • Computational Fourier optics to study the reliability of ray-tracing through optical turbulence
  • Existing turbulent open-path dual frequency comb measurements under analysis

Aero-optical measurement strategy


Our MURI effort includes close links between measurements, modeling, and theory to achieve the most comprehensive understanding of the dynamics underlying stratospheric turbulence, the impacts of turbulence and particles on hypersonic vehicle boundary layer stability, and turbulence influences on aero-optic propagation. Model results will contribute to specification of routine and focused measurement capabilities and strategies; evolving measurements will help guide new modeling studies; and current and new modeling results will be used as inputs to evaluate turbulence impacts on vehicle boundary layer stability and aero-optic propagation. A flow chart showing the expected links among program elements is shown below:

Figure 10 Graph